Question

# A child is moving on a skateboard with a speed of 2 msâˆ’1. After a force acts on him, his speed becomes 3 msâˆ’1. Calculate the work done by the force, if the mass of the child is 20 kg.

A

1 J

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B

10 J

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C
20 J
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D
320 J
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Solution

## The correct option is B 10 J Given: initial velocity of the child, u=2 ms−1, final velocity, v=3 ms−1, and mass, m=20 kg. Initial kinetic energy =mu22 Final kinetic energy =mv22 Change in kinetic energy =mv22–mu22 ⇒m×(v2−u2)2=20×(9–4)2=50 J Work done by force = change in kinetic energy of the child Therefore work done by the force is 50 J

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